1. Field of the Invention
The present invention relates to methods for producing tomato products such as tomato juice, tomato essence etc., more particularly this invention provides a method for producing tomato juice under a certain quality standard from various tomatoes having different characteristics, and also a method for producing new tomato essence retaining less amount of components giving out a green odor.
2. Description of the Prior Art
Practical means to do something for taste adjustment of tomato juice is only adding salt during the process. Therefore, the quality of tomato juice is strongly influenced by the quality of raw tomatoes. Since a balance among sugar content, acidity and salt contents is a basic factor to decide the goodness of the taste of tomato juice, a way to gain the proper balance from raw material and keep it during the processing is a great concern for the people who are in charge of production of tomatoes and processing them. Furthermore, since another factor, the consistency also gives a great influence on the taste of tomato juice, control of the taste is possible by adjusting the consistency during processing.
According to our study, it was found that mouth feeling of tomato juice is classified in three different types based on a principle analysis shown in Table 1.
TABLE 1 ______________________________________ relative precipitate serum weight Type sensory expression viscosity ratio ______________________________________ A rich body, and a heavy high large feeling to swallow B rich body, and a light low large feeling to swallow C poor body, and a light low small feeling to swallow ______________________________________
The relative serum viscosity is a relative number of the flow time of a sample to that of water in Cannon-Fenske viscometer. The weight of precipitate obtained after centrifugation at 12800.times.g at 4.degree. C. for 30 minutes was compared to the original sample weight in a ratio and the ratio was shown as the precipitate weight ratio in terms of a percent. This parameter shows the amount of dietary fibers and its water holding capacity, and also implies the bodiness of tomato juice and the swelling volume of fibers in the intestines. As shown in table 1, a pair of a low relative serum viscosity and a high precipitate weight ratio should be obtained in order to produce B type of tomato juice which has a rich bodiness but a light feeling to swallow. This B type provides dietary fibers more to the consumers without making them feel the texture of juice too heavy.
A usual processing method of tomato juice showing B type of rheological property is to crush tomatoes, heat them at a low temperature with a tubular heater and extract the juice intensively with commercially available extractors such as screw type, paddle type or butterfly type. However, this processing method allows lipoxygenases and pectin-degrading enzymes of tomatoes work strongly, and these reactions generate a strong green odor and produce a strong synelysis, resulting in a poor tomato juice. In particular the use of firm tomatoes makes it difficult to produce B type of tomato juice because of the above problems.
On the other hand, commercial industries employ two ways to manufacture tomato juice. One is seasonal pack that extracts the juice from raw tomatoes and manufactures the final product during the season. The other way is reconstituted pack which concentrates the tomato juice during the season, stores them and later on dilutes and prepares tomato juice during post-harvest season. It is well recognized that reconstituted tomato juice is inferior to the seasonal pack.
As one of the methods to improve the quality of reconstituted tomato juice, fortifying natural tomato essence has been already reported. However the technology to recover tomato essence upon a certain design has not yet been developed. It is well known that tomato fruits biosynthesize various tomato aroma components in their metabolic ripening pathways and also generate new aroma constituents through various enzymatic reaction in crushed tomatoes during processing. Important aroma components which are generated during processing of tomatoes are C.sub.6 compounds such as n-hexanol, cis-3-hexenol, etc. These show a sensory characteristics providing so-called "freshness" as long as they present at a certain concentration. High concentration of those components above a certain level inversely gives unfavorable aroma profile such as green odor. C.sub.6 compounds will be concentrated in natural recovered tomato essence. However, a recovering method of essence which regulates the relative concentration of C.sub.6 compounds to those of other aroma compounds, or a processing method which recovers tomato essence containing strong intrinsic tomato aroma while depressing the green odor to a certain level, has not yet been found. At the same time, it is very difficult to separate C.sub.6 compounds only out of a recovered tomato essence and adjust the concentration later.